1. Field of the Invention
The invention relates to high voltage devices, and in particular to high voltage devices capable of preventing leakage current caused by inversion layer.
2. Description of the Related Art
A high voltage device is one of the most important devices utilized in highly integrated circuits and is a device that can sustain a higher voltage this is applied thereto. In general, the break down voltage of a high voltage device is higher than a regular device. For example, a regular device has an operating voltage range of about 5V, and a high voltage device has an operating voltage range from 40V˜100V. Typically, the high voltage device has a structure similar to that of a MOSFET. Erasable programmable read only memory (EPROM) and flash memory are two high voltage devices most often used in computers and electronics products.
FIG. 1A shows a conventional high voltage device, and FIG. 1B is a cross section of the high voltage device shown in FIG. 1A along the line AA′. As shown in FIG. 1A, a high voltage device 10 is formed on the substrate 12, in which isolation (STI) structure 14 defines active area (AA) 16, and poly gate structure 18 is disposed on the isolation structure 14 and the active area 16. As the poly gate structure 18 covers the isolation structure 14, inversion layer is induced at the edges of the active area 16 after a high temperature stress, conducting leakage current Ioff.